Vacuum gauge



Dec. 13, 1927.

J. W. LEGG VACUUM- GAUGE Filed Oct. 9. 1920 INVENATOR Jsgv/z &/

ATTORNEY WITNESSES: W

V termined fixed point.

r '35 ured would be imperfect gases and would. move slowly and avoiding the often en- Patented Dec. 13, 1927.

] UNITED STATES IPATENT', OFFICE.

JQsEP LEr WQLEGe, OFLWIILKINSBUBG,PENNSYLVANIA, ASSIGNOR 'rownstrrnerrousn" nmcrnrcamanurncrunme COMPANY, [A conrona'rron' orrENNsY vANIAQ,

, "vacuum GAUGE;

" Ap lication flled 'octob e'r 9, 1920. Serial No. 415,938.

This inventi'onrelates to means for meas-' thereof to construct a gauge which shall uring low pressures, commonlyv called Vacupractically obviate danger of breakage due 'umgauges, more especially to one which to improper manipulation or accidental .or utilizes the compression of a gas to measure sudden changes of pressure, which shall be 5 the original pressurethereofzeasy to manipulate and be practically auto Several types of vacuum gauges have been matic in its action. proposed heretofore, one of which has been In practicing my invention, ,1 provide a l in fairly common use. This gauge consisted "capillarytube, as formerly, arranged so that essentially of .acapillary tubecommunicat the tube may be placed in communication. 10 ing with the top of a bulb, the lower end of witha source of vacuum to be measured, but,

which was connected to anotherbulb 'conby providing additional features, I have taining mercury, by means of a flexible tube. been enabled to obviate inaccuracies intro- There was also a connection to the capillary duced by changes in atmospheric pressure-in tubeand its-bulb from a source ofvacuum readings-on the scale of the gauge. 'specifi-o 15 to be measured. f cally, I have so proportioned my apparatus When it was desired to determine a-that, when the gauge is in operative posi- 5 vacuum, the bulb containing mercury was .tion, the area of mercury in contact with low r d th t ommunication-was estabthe low pressure'or vacuum to be measured fi hed bet n th um to be measured is many times greater than the area subject -and the capillary tube and its bulb, after to the pressure of thev atmosphere. By

which the mercury bulb was raised to conmaking the ratio large, say 500 to 1,.evenexfine the gas in the capillary tube,and readtremevariations in atmospheric pressure, as ings were taken after'the level of mercury great as one inch of mercury, will, cause a in the capillary tube had arisen to aprede changein levelof the mercury exposed to V V j the vacuum of 1/500of an inch at the most. It will be seen that, in measuring various Since this error-is no greater than the error pressureswith such an instrument, the 'presin reading the scale, it may, for practical sure of the gas withinthe capillary tube purposes, be considered absent.

would vary by reason of the mercury being I have provided also means to preventa 30 caused to rise to the same point whatever suddenrush of mercury from one point in might be the pressure tobe measured. This the apparatusto another and have accomgave rise to avariable error in measurement "plished this by forming a constricted porsince the basis of the determination isa pertion in one, of the tubes through which the feet gas, whereas practically all gases measmercury must flow, thereby forcing it. to

not follow Boyles law. Such a gauge set countered difliculty of hammering and ting must be adjusted very carefully at each consequent'breaking of the apparatus. determination, and the'height of the mer- In order to increase the senstitiveness of cury reservoir" be changed to allow for my instrument, I have so arranged the parts 40 changes in atmospheric p'ress'uref It oftenthat a very large volume of gas obtained occurred that,'in measuring high vacuums from the sourceof vacuum to be measured 'with such a gauge, the sudden rush of meris compressed to a very small volume in the 'curyfrom one part'of the gauge to another capillary tube. To accomplish this, I form caused 'so-called hammering, whichfre: a bulb on the lower end of'the capillary'tube,

45 'quently broke the. apparatus, even in the the volume of the bulb and connectionsbehands of a skilled operator; I i jin 100 times or 1000 times orany' desired The resent invention is designed to eliminumber of times greater than the VQlllljfiQ of nate, the difliculties encountered in prior predetermined portion of the vacuum gauges, it being among the objects time which is ta constitute the gauge proper,

In the accompanying drawings forming a part hereof and m which similar rclcrencc characters denote similar parts,

and a tube 3, secured in the lower and ot bulb 2, extends downwardly nu-zrging into a smaller tube 4 of considerable length. The lower end of tube at is formed with a constricted portion Surrounding tube at and concentric therewith, a tube 6, the latter tube being closely adjacent to the tube at so that the area '7 between the inner and the outer tube is very small. 1

The tube 6 constitutes a downward extension of receptacle Ssecured to tube 3 at point 9. A alve 10 of suitable construction allows communication between receptacle 8 and a source 12 of a partial vacuum and also, at point 11, to the atmosphere, the valve being so constructed that the receptacle 8 may be. alternately connected to the partial. vacuum or to the air or be cutofi from both, at will.

A side tube 13 is secured in tube 3 ata 1 point slightly below bulb 2, the upper end of tube 13 terminatinp, in a chamber lethavinp; a tube '15 leading from the top thereof and adapted to be connected to a vacuum to be measured. A capillary tube 16 has its up per end opening into chamber 1-1 at a point above the higl'lest mercury level therein and its lower and opening into tube 13. A scale 17, suitably calibrated, is secured to the capillary tube 1, the upper closed end 18 of which is at the same level as the mercury 19 in tube 16 when the apparatus is in position for the determination of a vacuum. The relative volumes of capillary tube 1 and bulb 2, with its connections, are such that the volume from point 18 to zero point 20 is a predetermined 1: action, say 1/100 of the volume from point 18 to point 21 where tube 13 is connected into the system.

I11 order to place the apparatus in condition for measuring vacuums initially, receptacle 8 is filled with mercury to apoint somewhat below level 22, and tube 15 is connected to a vacuum. Stop valve 10 is opened to allow communication of receptacle 8 with the atmosphereythus forcingthe mercury in the receptacle down through space 7 and up into tube l, bulb 2 and chamber 1 1. Mercury is then added to receptacle Snntil the level 19 in capillary tube 16 is at the same height as the top 18 of capillary tube 1. It a predetermined and known vacuum had previously been established inchamber 1i and, therefore, capillary tube 1 andbulb 2, and the level 20 of mercury reached, this point may be set as the zero or starting point, and the pressure measured at this point be determined by simple calculations. The scale 17 between points 18 and 20 may then be calibrated by interpolating figures.

After the gauge has been calibrated, valve 10 is opened so that receptacle 8 connnunicates with partial vacuum 12 in order to d aw the mercury back into receptacle 8 to the normal level 22. In order to measure a vacuum, tube 15 is connected to the vacuum to be measured, valve 10 opened; to allowaccess of air into rece .tacleS, forcing mercury into bulb 2 and ciamber 14 until the level of mercury rises automatically to point- 19, the other mercury level in contact with the atmosphere being at point- 23; The lengths of tubes 4 and 6 are such that there is at. least 760 mm. between level 22 of mercury and constricted portion 5. This obviates any danger of the mercurylevel win tube 1, when vacuum is applied to receptacle 8 and atmospheric pressure is in tube 15,

from falling to a point below the open end of tube 4 and thus suddenly introducing air into receptacle 8 through tube 6 and thus breaking the apparatus by mercury hammer. The pressure in the vacuum chamber maybe read directly from scale 17. In order to place the apparatus in position for measuring another vacuum, it is merely necessary to open valve 10 to the partial vacuum 12 and allow the mercury level to dropbcyond point 21. i l

By means of this apparatus, it is apvcry simple matter to measure vacaumssinceall that is necessary isto connecttube lfi to the source of vacuumand open valve 10. The readings are very accurate and are unaffected by changes in atmospheric pressure, since the area 23 of mercury is very small compared to the arcafia. There is no dangcr of breakage since it impossible for mercuryto flow swiftly by reason of the constriction 5 in the lowerend of tube ,4.

Although I have shown and described a specific embodiment of my invention, it is obvious that my invention is not limited to the exact structure shown, as various changes may be made in details of the apparatus without departing from the principlcs involved. For instance, instead of forming the constricted portion at the lower tube, the upper endv thereof being closed and the lower cndlcomnnjmicating witlra bulb, another tube secured in the lowercnd of said bulb and extending' downwardlyfor a distance sufficient to prevent air from entering the same, .an elongated receptacle surrounding said lattcr tube throughout the length thereof, said receptacle and tube having a restricted communication at their lower ends, a branched tube in unrestricted communication with the-upper portion of said latter tube and with a chamber communicating with a vacuum to be measured, and

means in said receptacle cooperating with 'said tube for preventing a rapid flow of JOSEPH w. LEGG; 

